This invention relates to a brake control apparatus for use in a vehicle such as a automobile, and more particularly, to a brake control apparatus for controlling a pressure force of a brake pad in accordance with rotation of wheels to prevent the wheels from locking in a vehicle which presses the brake pad to a brake disk in accordance with a braking operation to brake the wheels.
In general, a disc brake is known which applies a brake to wheels by friction between a braking pad and a brake disk in a vehicle such as an automobile. More particularly, actuation of a brake pedal is transmitted to a caliper with the aid of a pressure of brake oil on applying the brake to the wheels in the vehicle, in order to press the brake pad to the brake disk. As a result, the brake disc applies the brake to the wheels in accordance with the friction between the brake pad and the brake disk.
On the other hand, it will be assumed that a harsh braking is applied in the vehicle when the vehicle runs on a slippery road surface on the basis of rainfall or snowfall. The wheels of the vehicle may become a locking state when a braking force exceeds a friction force between the wheels and a road surface. The locking state means that the wheels stops rotating but a car body runs forward. In case where locked wheels are front wheels, it is difficult to steer the vehicle. In case where the locked wheels are rear wheels, an attitude of the car body becomes unstable.
Under the circumstances, a sort of anti-lock brake apparatuses are developed and are realized. In each of the anti-lock brake apparatuses, the wheels are prevented from locking by brake actuation such as a pumping brake actuation to keep a steering ability and to make the attitude of the car body become stable. More specifically, the brake oil pressure is decreased at once in order that the pressure force of the brake pad reduces to the brake disk in a conventional one of the anti-lock brake apparatuses, when detection is made at the instant preceding the locking of the wheels or at the initial locking of wheels. When the pressure force of the brake pad reduces to the brake disk, the braking force is slightly less than a friction force between the road surface and the wheels. As a result, the wheels return to rotate. After that, the brake oil pressure is increased in order to increase the pressure force of the brake pad. A cycle is repeated in which the pressure force of the brake pad is decreased and is increased. As a result, the lock of the wheels is released.
However, the conventional anti-brake apparatus uses, as the brake pad of the ant-brake, the brake pad, which is used in a usual brake operation in order to carry out the anti-brake operation. Therefore, it is impossible to carry out both of the usual brake operation and the anti-brake operation at the same time in the conventional anti-brake apparatus although it is possible to carry out either one of the usual brake operation and the anti-brake operation. In this event, the usual brake operation is carried out at first in the conventional anti-brake apparatus when the brake pedal is pressed. When detection is made at the instant preceding the locking of the wheels or at the initial locking of wheels, the usual brake operation is turned into the anti-brake operation in the conventional ant-brake apparatus. Therefore, it is difficult to prevent the wheels from locking although if it is possible to early release the wheels from locking in the conventional anti-brake apparatus. When the timing is advanced at which the usual brake operation is turned into the anti-brake operation, the duration of the usual brake operation becomes short. As a result, the braking time duration becomes long and the braking distance also becomes long.
In addition, a force, which produced on the basis of variation of the oil pressure in the caliper, is transmitted to the brake pedal when the conventional anti-brake apparatus. Such a transmission will be called a kickback. As a result, the brake pedal vibrates with quick steps. Inasmuch as the brake pedal vibrates with quick steps in no concern to the driver""s intension, the driver has unmoral feeling. Even if a light or a sound sends a notice when the kickback occurs, it is difficult for the driver to remove the unmoral feeling.
It is therefore an object of this invention to provide a brake control apparatus capable of preventing the wheels from locking without increasing braking time duration and a braking distance.
It is another object of this invention to provide a brake control apparatus capable of preventing the occurrence of a kickback.
Other objects of this invention will become clear as the description proceeds.
According to a first aspect of this invention, there is provided a brake control apparatus comprising a brake disk rotating with a wheel, a main brake mechanism for pressing a main friction member to the brake disk in accordance with an operation of a brake operating member to brake the wheel, lock detecting means for detecting whether or not the wheel becomes an instant condition preceding a locking or an initial condition of the locking to produce a lock detection signal when the wheel becomes the instant condition preceding the locking or the initial condition of the locking, main brake control means for controlling the main brake mechanism to make the main brake mechanism temporarily reduce a main press force which is applied from the main friction member to the brake disk. The brake control apparatus comprises a subsidiary brake mechanism for pressing a subsidiary friction member to the brake disk to brake the wheel and first subsidiary brake control means for controlling the subsidiary brake mechanism to make the subsidiary brake mechanism repeat a variation cycle during the operation of the brake operating member before the first subsidiary brake control means receives the lock detection signal. The subsidiary brake mechanism increases a subsidiary press force after reducing the subsidiary press force in the variation cycle. The subsidiary press force is applied from the subsidiary friction member to the brake disk.
When operating the brake-operating member, the main brake mechanism makes presses the main friction member to the brake disk, which rotates with the wheel, in accordance with the operation of the brake-operating member. On the basis of the friction between the brake disk and the main friction member that is based on the press, the rotation of the wheel is stopped. When the braking force becomes greater than the friction force between the wheel and the road surface and when the wheel becomes the instant condition preceding the locking or the initial condition of the locking, the lock detecting means detects that the wheel becomes the instant condition preceding the locking or the initial condition of the locking. The lock detecting means produces the lock detection signal. In accordance with the lock detection signal, the main brake control means controls the main brake mechanism. Under the control, the main press force of the main friction member increases after reducing temporarily. As a result, an ant-lock braking operation is carried out which is similar to a pumping brake operation.
By the way, first subsidiary brake control means controls the subsidiary brake mechanism during the operation of the brake operating member before the first subsidiary brake control means receives the lock detection signal. More particularly, the subsidiary brake mechanism repeats the variation cycle while the main friction member continues to be pressed to the brake disk, before the main brake control means starts controlling the main brake mechanism. The subsidiary press force increases after reduction. As readily understood from the above description, the wheel is supplied with a main braking force and a subsidiary braking force at the same time. The main braking force is based on an usual braking operation according to the main brake mechanism. The subsidiary braking force is based on an intermittent braking operation according to the subsidiary brake mechanism. The intermittent braking operation may be a pumping brake operation similar to the anti-lock braking operation. As a result, it is possible to hardly make an occurrence of locking in comparison to only the usual braking operation. In addition, a braking time duration and a braking distance do not become long inasmuch as a large braking force is applied to the wheel as compared with a timing operation at which the usual braking operation is switched to the anti-lock braking operation in an early stage.
According to a second aspect of this invention, the brake control apparatus further comprises brake operation detecting means for detecting the operation of the brake-operating member to produce a brake operating detection signal. The first subsidiary brake control means controls the subsidiary brake mechanism to make the subsidiary brake mechanism start the variation cycle when the first subsidiary brake control means receives the brake operating detection signal.
When the brake operation detecting means detects the operation of the brake operating member, the first subsidiary brake control means controls the subsidiary brake mechanism to make the subsidiary brake mechanism start the variation cycle. The first subsidiary brake control means makes the subsidiary brake mechanism carry out the intermittent braking operation with the main brake mechanism carrying out the usual braking operation based on the operation of the brake operating member.
According to a third aspect of this invention, the first subsidiary brake control means controls the subsidiary brake mechanism to make the subsidiary brake mechanism finish the variation cycle when the first subsidiary brake control means receives the lock detection signal.
When the lock detecting means detects that the wheel becomes the instant condition preceding the locking or the initial condition of the locking, the first subsidiary brake control means controls the subsidiary brake mechanism to make the subsidiary brake mechanism finish the variation cycle. The first subsidiary brake control means makes the subsidiary brake mechanism carry out the intermittent braking operation until the main brake mechanism finishes the usual braking operation based on the operation of the brake-operating member.
According to a fourth aspect of this invention, the brake control apparatus further comprises a second subsidiary brake control means for controlling the subsidiary brake mechanism to make the subsidiary brake mechanism repeat the variation cycle on receiving the lock detection signal before the main brake control means starts controlling the main brake mechanism after the first subsidiary brake control means finishes controlling the subsidiary brake mechanism.
After the first subsidiary brake control means finishes controlling the subsidiary brake mechanism, the second subsidiary brake control means for controlling the subsidiary brake mechanism in a following manner before the main brake control means starts controlling the main brake mechanism. When the lock detecting means detects that the wheel becomes the instant condition preceding the locking or the initial condition of the locking, the subsidiary brake mechanism increases the subsidiary press force of the subsidiary friction member after the subsidiary brake mechanism temporarily reduces the subsidiary press force of the subsidiary friction member. The variation cycle having the reduction and the increase of the subsidiary press force is repeated so that the subsidiary brake mechanism carries out the anti-lock braking operation. In other words, the instant when the lock detecting means detects that the wheel becomes the instant condition preceding the locking or the initial condition of the locking, the main brake mechanism does not carry out the anti-lock braking operation and the subsidiary brake mechanism carries out the anti-lock braking operation at first. After this, the main brake mechanism starts carrying out the anti-lock braking operation. Therefore, the anti-lock braking operation is carried out by the subsidiary brake mechanism at first in case where the braking force based on the subsidiary press force of the subsidiary friction member is less than the braking force based on the main press force of the main friction member. In case where the locking is not released by the above-mentioned operation, the anti-lock braking operation is carried out by the main brake mechanism.
According to a fifth aspect of this invention, the main brake mechanism comprises a main transmission tube for use in transmitting the main friction member with a fluid pressure based on the operation of the brake operating member. The subsidiary brake mechanism comprises a subsidiary transmission tube for use in transmitting the subsidiary friction member with the fluid pressure to operate the subsidiary friction member in accordance with the fluid pressure.
When the brake-operating member is operated, the operating force is transmitted to the main friction member through the main transmission tube by the fluid pressure. The main friction member is pressed to the brake disk on the basis of the transmitted fluid pressure so that the main friction member applies a brake to the wheel on the basis of the friction between the main friction member and the brake disk. In addition, the anti-lock braking operation is carried out by the main brake mechanism when the fluid pressure is varied which is applied to the main friction member. A reverse force based on the variation of the fluid pressure is also transmitted as a kickback to the brake-operating member.
On the other hand, the fluid pressure is applied to the subsidiary friction member through the subsidiary transmission tube during the operation of the brake-operating member. The subsidiary friction member is pressed to the brake disk on the basis of the transmitted fluid pressure so that the subsidiary friction member applies a brake to the wheel on the basis of the friction between the subsidiary friction member and the brake disk. Inasmuch as the subsidiary transmission tube is independent of the main transmission tube, the operating force of the brake-operating member is not directly applied to the subsidiary transmission tube. Therefore, the reverse force is not transmitted to the brake-operating member even if the fluid pressure varies. Furthermore, the reverse force based on the variation of the fluid pressure is not transmitted to the brake-operating member in a manner similar to the intermittent braking operation in case where the anti-lock braking operation is carried out by the subsidiary brake mechanism.
According to a sixth aspect of this invention, the brake control apparatus further comprises fluid pressure detecting means for detecting the fluid pressure in the main transmission tube to produce a pressure detection signal representative of the fluid pressure. The first subsidiary brake control means includes press force varying means for varying the subsidiary press force in accordance with the pressure detection signal.
In case where the first subsidiary brake control means controls the subsidiary brake mechanism, the fluid pressure is detected in the main transmission tube by the fluid pressure detecting means. The fluid pressure is different in accordance with the operation of the brake-operating member, which is operated by a driver. The fluid pressure is adjusted in the subsidiary transmission tube in accordance with the detected fluid pressure. The fluid pressure in the subsidiary transmission tube is applied to the subsidiary friction member. The subsidiary press force, which is applied from the subsidiary friction member to the brake disk, is based on the detected fluid pressure detected by the fluid pressure detecting means, namely, the operation of the brake operating member. Therefore, the subsidiary friction member is pressed to the brake disk by the subsidiary press force appropriate to an operating condition of the brake operating member which is operated by the driver, in case where the intermittent braking operation is carried out by the subsidiary brake mechanism, although the operating condition is different on the basis of the running condition of the vehicle. The operating condition may be, for example, an operating amount and/or operating speed.
According to a seventh aspect of this invention, the main friction member is positioned at a main region of the brake disk. The subsidiary friction member is positioned at an intermediate region of the brake disk. The intermediate region is different from the main region and an opposite region, which is opposed to the main region across a rotation center of the brake disk.
When the main friction member is pressed to the brake disk, the braking force is operated to a contact portion between the main friction member and the brake disk and another braking force is operated to the opposite region which is oppose to the main friction member across the rotation center of the brake disk, in order to balance the braking force. It will be assumed that the subsidiary friction member is positioned at the opposite region. The braking forces based on both of the main friction member and the subsidiary friction member are operated to a same region of the brake disk at the same time in case where the subsidiary friction member is pressed to the brake disk. On the basis of a synergistic effect based on both of the braking forces, an excessive force greater than a sum of both of the braking forces is operated to the brake disk. On the other hand, the subsidiary friction member is positioned a region apart from the opposite region in this invention. Therefore, both of the braking forces are scattered so that both of the braking forces are applied to the brake disk even if both of the main friction member and the subsidiary friction member are pressed to the brake disk at the same time. As a result, the force greater than the sum of both braking forces is not operated to the brake disk.
According to an eighth aspect of this invention, the subsidiary friction member is positioned near the opposite region in the intermediate region.
The subsidiary friction member is positioned apart from the main friction member in the intermediate region to be pressed to the brake disk. In the intermediate region, a region, at which the subsidiary friction member is not positioned, is always exposed to the atmosphere. The exposed region is used as a heat radiation region. The heat based on the friction between the main friction member and the brake disk or between the subsidiary friction member and the brake disk is dissipated from the heat radiation region to the atmosphere.